To use the CMTAT, we recommend the latest audited version, from the Releases page. Currently, it is the version v2.3.0

The CMTA token (CMTAT) is a framework enabling the tokenization of securities in compliance with Swiss law. This repository provides CMTA's reference implementation of CMTAT for Ethereum, as an ERC-20 compatible token.

The CMTAT is an open standard from the Capital Markets and Technology Association (CMTA), which gathers Swiss finance, legal, and technology organizations. The CMTAT was developed by a working group of CMTA's Technical Committee that includes members from Atpar, Bitcoin Suisse, Blockchain Innovation Group, Hypothekarbank Lenzburg, Lenz & Staehelin, Metaco, Mt Pelerin, SEBA, Swissquote, Sygnum, Taurus and Tezos Foundation. The design and security of the CMTAT was supported by ABDK, a leading team in smart contract security.

The preferred way to receive comments is through the GitHub issue tracker. Private comments and questions can be sent to the CMTA secretariat at admin@cmta.ch. For security matters, please see SECURITY.md.

Note that CMTAT may be used in other jurisdictions than Switzerland, and for tokenizing various asset types, beyond equity and debt products.

The CMTAT supports the following core features:

• Basic mint, burn, and transfer operations
• Pause of the contract and freeze of specific accounts

Furthermore, the present implementation uses standard mechanisms in order to support:

• Upgradeability, via deployment of the token with a proxy
• "Gasless" transactions
• Conditional transfers, via a rule engine

This reference implementation allows the issuance and management of tokens representing equity securities. It can however also be used for other forms of financial instruments such as debt securities.

You may modify the token code by adding, removing, or modifying features. However, the core modules must remain in place for compliance with Swiss law.

To deploy CMTAT without a proxy, in standalone mode, you need to use the contract version CMTAT_STANDALONE.

The CMTAT supports deployment via a proxy contract. Furthermore, using a proxy permits to upgrade the contract, using a standard proxy upgrade pattern.

The contract version to use as an implementation is the CMTAT_PROXY.

Please see the OpenZeppelin upgradeable contracts documentation for more information about the proxy requirements applied to the contract.

Please see the OpenZeppelin Upgrades plugins for more information about plugin upgrades in general.

Note that deployment via a proxy is not mandatory, but is recommended by CMTA.

Factory contracts are available to deploy the CMTAT with a beacon proxy or a transparent proxy.

CMTAT_BEACON_FACTORY.sol

CMTAT_TRANSPARENT_FACTORY.sol

Beacon Proxy factory: the factory will use the same beacon for each beacon proxy. This beacon provides the address of the implementation contract, a CMTAT_PROXY contract. If you upgrade the beacon to point to a new implementation, it will change the implementation contract for all beacon proxy.

Transparent Proxy factory: the factory will use the same implementation for each transparent proxy deployed. Each transparent proxy has its owned proxy admin, deployed inside the constructor of the transparent proxy. Each transparent proxy can upgrade their implementation to a new one independently and without impact on other proxies.

The CMTAT supports client-side gasless transactions using the Gas Station Network (GSN) pattern, the main open standard for transfering fee payment to another account than that of the transaction issuer. The contract uses the OpenZeppelin contract ERC2771ContextUpgradeable, which allows a contract to get the original client with _msgSender() instead of the fee payer given by msg.sender while allowing upgrades on the main contract (see Deployment via a proxy above).

At deployment, the parameter forwarder inside the CMTAT contract constructor has to be set with the defined address of the forwarder. Please note that the forwarder can not be changed after deployment, and with a proxy architecture, its value is stored inside the implementation contract bytecode instead of the storage of the proxy.

Please see the OpenGSN documentation for more details on what is done to support GSN in the contract.

CMTAT initially supported a kill() function relying on the SELFDESTRUCT opcode (which effectively destroyed the contract's storage and code). However, Ethereum's Cancun upgrate (rolled out in Q1 of 2024) will remove support for SELFDESTRUCT (see EIP-6780).

The kill() function will therefore not behave as it used to once Cancun is deployed.

The alternative function is the function deactivateContract, introduced in the version v2.3.1 inside the PauseModule, to deactivate the contract. This function set a boolean state variable isDeactivated to true and puts the contract in the pause state. The function unpauseis updated to revert if the previous variable is set to true, thus the contract is in the pause state "forever".

The consequences are the following:

• In standalone mode, this operation is irreversible, it is not possible to rollback.
• With a proxy, it is still possible to rollback by deploying a new implementation.

Here the list of the differents modules with the links towards the documentation and the main file.

Generally, these modules are required to be compliant with the CMTA specification.

Generally, these modules are not required to be compliant with the CMTA specification.

The RuleEngine is an external contract used to apply transfer restriction to the CMTAT through whitelisting, blacklisting,...

This contract is defined in the ValidationModule.

An example of RuleEngine is also available on Github.

Here is the list of the different version available for each CMTAT version.

This contract acts as a controller and can call different contract rule to apply rule on each transfer.

A possible rule is a whitelist rule where only the address inside the whitelist can perform a transfer

Since the version 2.4.0, the requirement to use a RuleEngine are the following:

The RuleEngine has to import an implement the interface IRuleEngine which declares the function operateOnTransfer.

This interface can be found in ./contracts/interfaces/engine/IRuleEngine.sol.

Before each transfer, the CMTAT calls the function operateOnTransfer which is the entrypoint for the RuleEngine.

The AuthorizationEngine is an external contract to add supplementary check on the functions grantRole and revokeRolefrom the CMTAT.

This contract is managed in the AuthorizationModule.

The AuthorizationEngine has to import an implement the interface IAuthorizationEngine which declares the functions operateOnGrantRole and operateOnRevokeRole

This interface can be found in ./contracts/interfaces/engine/IAuthorizationEngine.sol.

Please see SECURITY.md.

See the code in modules/security.

Access control is managed thanks to the module AuthorizationModule.

The contracts have been audited by ABDKConsulting, a globally recognized firm specialized in smart contracts security.

Fixed version : 1.0

Fixes of security issues discovered by the initial audit were reviewed by ABDK and confirmed to be effective, as certified by the report released on September 10, 2021, covering version c3afd7b of the contracts. Version 1.0 includes additional fixes of minor issues, compared to the version retested.

A summary of all fixes and decisions taken is available in the file CMTAT-Audit-20210910-summary.pdf

Fixed version : v2.3.0

The second audit covered version 2.2.

Version v2.3.0 contains the different fixes and improvements related to this audit.

The report is available in ABDK_CMTA_CMTATRuleEngine_v_1_0.pdf.

You will find the report produced by Slither in

A code coverage is available in index.html.

As with any token contract, access to the owner key must be adequately restricted. Likewise, access to the proxy contract must be restricted and seggregated from the token contract.

Here a summary of the main documents:

CMTA providers further documentation describing the CMTAT framework in a platform-agnostic way, and covering legal aspects, see

• CMTA Token (CMTAT)
• Standard for the tokenization of shares of Swiss corporations using the distributed ledger technology

The code is copyright (c) Capital Market and Technology Association, 2018-2024, and is released under Mozilla Public License 2.0.